The invention relates to a method and a device for optical measuring of small particles, such as grains from cereals and like crops, for analysis of the quality of the particles.
Inspection of different kinds of cereals and other crops is today made all over the world to determine the quality of the cereals in commercial transactions and handling. The inspection aims at examining a selected representative sample from a large consignment and determining the presence of non-desirable grains and particles. The non-approved grains and particles are classified and the quantity of each class is determined. Owing to the distribution of the various grains, the sample and, thus, the consignment will be given a grading which is a decisive factor in connection with payment and handling of the consignment.
Today most cereal inspections are carried out entirely manually. A skilled inspector has often passed through a comprehensive education of many years. Nevertheless there are great deviations in the analyses/classifications between different inspectors owing to, among other things, personal assessments and varying conditions of lighting. Deviations also occur in each individual inspector because of, for example, the degree of fatigue.
It is therefore desirable for the methods of analysis to be automated to reduce the deviations and create a more stable situation with a more transparent grading process. For an exact grading of the sample, the grains must be separated from each other to allow each individual grain to be classified. This can be made either by physical separation or by means of digital image processing.
Thus, use is presently made of certain optical measuring methods for analysis of the quality of the grains. These measuring methods are based on a grain being illuminated, whereupon some sort of detection is made of the light emitted from the grain for analysis of the quality of the grain. The illumination may vary significantly regarding, for example, from which direction the grain is illuminated, which wavelength is used, etc. The detection may vary in respect of whether e.g. reflected light, transmitted light or diffuse light is detected.
Instruments using one or more of these optical measuring methods have some kind of physical sorting out of the grains so that only one grain at a time is measured. It should, however, not be necessary to interrupt the feeding of grains each time a grain is to be measured. This means that it must be possible to optically measure moving grains. This places great demands on the optical detection to prevent the movement of the grain from spoiling the measurement. An extremely quick detector must be used, which causes great costs, or the feeding of samples must be carried out so slowly that a less expensive, slower detector will manage, which results in a long time of waiting between measurements of two grains.
A quick detector also involves peripheral equipment, which requires a great deal of space. Since the time of exposure must be very short, the detector also requires that large amounts of light be available, and this requirement is difficult to satisfy.
To prevent movement blur from arising, a grain cannot move more than extremely marginally during the measuring time of the detector. The measuring time of the detector and the distance a grain can move during the measurement thus decide the speed at which the samples can be fed. For an ordinary detector, this means a very low speed and unacceptable analyzing times.
A compromise could be to vary the speed of the feeding, in such manner that the grains are fed quickly when no measurement occurs, and slowly during measurement. This, however, causes wear on mechanical components feeding the samples since acceleration and retardation occur constantly. This also places demands on the control so that the correct speed is kept up during and between measurements.
An object of the present invention is to provide a quick automatic method for optical measurement of particles for analysis. A further object is to solve the above problems and provide optical measurements of particles fed at a high speed, using conventional, relatively inexpensive detectors.
The objects of the invention are achieved by means of a device according to claim 1 and a method according to claim 14. Further advantages of the invention are evident from dependent claims 2-13 and 15-27.
Thus, the invention provides a device for optical measuring of small particles, such as grains from cereals and like crops, for analysis of the quality of the particles. The device comprises a sample-feeding carrier, which is adapted to take up particle samples, which each comprise at least one particle, in sample holders and transport the particle samples to a place for optical measurement, a mirror-supporting means, which follows the movement of the carrier and has a mirror for each sample holder, a device for illuminating a particle sample when this is positioned for optical measurement, and a detector which is sensitive to electromagnetic radiation for recording at least one result of an optical measurement of the illuminated particle sample. A mirror in the mirror-supporting means reflects the particle sample, so that a mirror image thereof stands essentially still seen from the detector, when the measurement is being recorded, owing to the fact that the mirror image of the particle sample falls on a center axis of the movement of the mirror-supporting means.
This design implies that the time of exposure can be extended significantly in the detector since the mirror image of the particle stands still. The extended time of exposure then causes no problems with movement blur and conventional detectors can be used. Particles can thus be fed at a high speed, which results in a high measuring speed. By the mirror image standing essentially still is meant that no translational movement occurs, but only a small degree of turning of the mirror image, owing to the movement of the mirror in front of the detector. This turning, however, is so small that no or very little movement blur arises.
According to a preferred embodiment, the sample-feeding carrier is adapted to feed the particle samples during continuous movement.
Since the particles can be fed at a high speed without causing movement blur in the detector, there is no need for a higher feeding speed between the measurements. The continuous movement means that the wear on mechanical components in the device is insignificant.
The detector is preferably an image-recording means, which records an image of the particle sample in the optical measurement. An image contains such an amount of information about the particle sample that it can be analyzed in respect of several properties on the basis of one measurement.
The device advantageously comprises a means for image analysis of the recorded image, an image of a particle sample, which comprises several particles, being divisible, with the aid of the means for image analysis, into images of one particle each. As a result, several particles can be analyzed on the basis of one image. The device will not be dependent on the condition that only one particle at a time is fed to the optical measurement.
The image-recording means conveniently is a digital camera. This means that an image of whole particles is recorded and image analysis can be used to analyze parts of the particles. No averaging as regards the light from the particle occurs, which could conceal defects or make the discovery of defects difficult. The digital camera produces an image in digital format, which is needed for the image analysis.
According to a preferred embodiment, the sample holders are adapted to take up only one particle. This means that a physical separation of the particles is obtained. In case of several analyses of the same particle using different illumination techniques, a physical separation is preferred.
The carrier is preferably circular and rotates to feed the particle samples. This ensures easy feeding of samples, and the feeding frequency can easily be made constant.
According to a further preferred embodiment, the mirror-supporting means and the carrier are interconnected by a central shaft and thus follow each other""s movements. This means that exact following of the movements of the particle samples can easily be provided. Exact following is important for the mirror image to stand still on the center axis of the movement.
The mirrors in the mirror-supporting means are preferably arranged at an angle of 45xc2x0 to the center axis, the distance between the particle sample and the associated mirror being the same as the distance between the mirror and the center axis for the mirror image of the particle sample to fall on the center axis. As a result, the detector is oriented perpendicular to the center axis for it to perceive the mirror image of the sample on the center axis. This provides a good position of the detector, which can then easily be adjusted correctly in terms of angle and which can also use the same stand as the carrier and the mirror-supporting means.
The sample holders of the carrier conveniently comprises indentations which offer a space for a particle sample. Thus the particles fall into the indentations when positioned under the particles. This results in an easy way of taking up particles in the sample holders.
According to a preferred embodiment, the sample holders of the carrier comprise through holes in the carrier and a lower particle holding disk which prevents the particles from falling through the holes, the holes and the particle holding disk thus offering a space for a particle sample. Also this embodiment results in an easy way of taking up particle samples in the sample holders. Moreover, the sample holders can easily be emptied by an emptying hole being arranged in the particle holding disk. When a full sample holder arrives at the emptying hole, the particle sample falls out of the sample holder by there being no bottom in the sample holder any longer.
According to another embodiment, the device has a means for generating a subatmospheric pressure on the underside of the carrier, the sample holders of the carrier comprising holes to which particle samples are made to adhere by the subatmospheric pressure. This means that a hole cannot possibly take up a plurality of particles at a time, which ensures the feeding of only one particle at a time.
A plurality of places for optical measurement, which each have a detector, are advantageously arranged in the device, and the illumination can be varied between the places for different analyses. This means that the particles can be analyzed in respect of several different properties in the same sorting out of the particles. The advantages of the device having a long time of exposure in spite of a high feeding speed can be used in all recordings of images.
The objects of the invention are also achieved by a method for optical measuring of small particles, such as grains from cereals and like crops, for analysis of the quality of the particles. The method comprises the steps of feeding particle samples which each comprise at least one particle, to a place for optical measurement, following the movement of a particle sample with a mirror in such manner that, in the place for optical measurement, a mirror image of the particle sample falls on a center axis of the movement of the mirror, illuminating the particle sample when located in the place for optical measurement, and recording at least one result of an optical measurement of the illuminated particle sample by means of a detector which is sensitive to electromagnetic radiation. The mirror image of the particle sample stands essentially still seen from the detector, when the measurement is being recorded, owing to the fact that the mirror image of the particle sample falls on the center axis of the movement. The method provides an automatic technique of recording, quickly and with conventional detectors, results of optical measurements for analysis of particles. The particles can be fed at a high speed, without making it too difficult for conventional equipment to satisfy the requirements as to a minimum time of exposure in the detector.
The method preferably comprises the step of analyzing the recorded image by means of image analysis to determine the quality of the particle sample. This means that the analysis can occur directly in the recording of the image, and a sample result can be obtained from the device, quickly and on the spot.